Intrinsic photogeneration of long-lived charges in a donor-orthogonal acceptor conjugated polymer

Shaikh, Jordan; Congrave, Daniel G.; Förster, Alex; Minotto, Alessandro; Cacialli, Franco; Penfold, Thomas J.; Bronstein, Hugo; Clarke, Tracey M.

doi:10.1039/d1sc00919b

Cited by 6 publications

(3 citation statements)

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“…There is a rise in the C 2 C 6 triplet from 1 to 10 μs, reaching a plateau at ∼20 μs, then finally decaying monoexponentially with a notably long lifetime of 450 μs. This is 2 orders of magnitude longer than the triplet lifetime of C 16 and 2–3 orders of magnitude longer than the triplets of well-known polymers with a similar bandgap such as PCDTBT, APFO3, and IF8TBTT, and over 4 times longer than the low-triplet-energy small-molecule rubrene. , Table S1 compares the triplet lifetime obtained in this work with small molecules and polymers with different bandgaps seen in the literature. ,,,− The rise in triplet population on the μs timescale for C 2 C 6 indicates that these triplets are not formed from standard intersystem crossing. Instead, they are formed upon a bimolecular charge recombination process, as can be observed by the C 2 C 6 bimolecular polaron decay kinetics matching the rise of the triplets (Figure S4).…”

Section: Resultsmentioning

confidence: 60%

Generating Long-Lived Triplet Excited States in Narrow Bandgap Conjugated Polymers

et al. 2023

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Narrow bandgap conjugated polymers are a heavily studied class of organic semiconductors, but their excited states usually have a very short lifetime, limiting their scope for applications. One approach to overcome the short lifetime is to populate long-lived triplet states for which relaxation to the ground state is forbidden. However, the triplet lifetime of narrow bandgap polymer films is typically limited to a few microseconds. Here, we investigated the effect of film morphology on triplet dynamics in redemitting conjugated polymers based on the classic benzodithiophene monomer unit with the solubilizing alkyl side chains C 16 and C 2 C 6 and then used Pd porphyrin sensitization as a further strategy to change the triplet dynamics. Using transient absorption spectroscopy, we demonstrated a 0.45 ms triplet lifetime for the more crystalline nonsensitized polymer C 2 C 6 , 2−3 orders of magnitude longer than typically reported, while the amorphous C 16 had only a 5 μs lifetime. The increase is partly due to delaying bimolecular electron−hole recombination in the more crystalline C 2 C 6, where a higher energy barrier for charge recombination is expected. A triplet lifetime of 0.4 ms was also achieved by covalently incorporating 5% of Pd porphyrin into the C 16 polymer, which introduced extra energy transfer steps between the polymer and porphyrin that delayed triplet dynamics and increased the polymer triplet yield by 7.9 times. This work demonstrates two synthetic approaches to generate the longest-lived triplet excited states in narrow bandgap conjugated polymers, which is of necessity in a wide range of fields that range from organic electronics to sensors and bioapplications.

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Section: Resultsmentioning

confidence: 60%

Generating Long-Lived Triplet Excited States in Narrow Bandgap Conjugated Polymers

et al. 2023

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“…Key bistrimethyltin compounds 3 and 6 were synthesized according to the previous reports. [38][39][40] Stille coupling between compound 7 or 3 or 6 and compound 8 was carried www.advopticalmat.de out to produce di-aldehyde compound PT-CHO or SPT-CHO or tSPT-CHO. Subsequently, knoevenagel condensation between the di-aldehyde compounds and electron-withdrawing end group 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile (IC-2F) yielded target PT-4F, SPT-4F, and tSPT-4F, respectively.…”

Section: Resultsmentioning

confidence: 99%

Spiro‐Conjugation in Narrow‐Bandgap Nonfullerene Acceptors Enables Broader Spectral Response and Higher Detectivity for Near‐Infrared Organic Photodetectors

Shao

Lei

Cao

et al. 2023

Advanced Optical Materials

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Near‐infrared (NIR) organic photodetectors (OPDs) are competitive candidates for flexible electronics in biomedical imaging and optical communications applications. However, current OPDs still suffer from a low detectivity beyond 1000 nm and a high dark current at bias due to the lack of high‐performance narrow‐bandgap non‐fullerene acceptors (NFAs). In this study, spiro‐conjugated core donor (D) unit is adopted to construct NFAs, SPT‐4F and tSPT‐4F. Comparing with PT‐4F without spiro‐conjugation, the orthogonal spiro‐conjugated planes endow SPT‐4F and tSPT‐4F with more rigid conformation and thus superior intermolecular stacking, resulting in the enhanced absorption beyond 1000 nm. Impressively, tSPT‐4F based device gives the best performance with a dark current of 4.52 × 10−10 A cm−2 under reversed bias of −0.1 V, an external quantum efficiency (EQE) response over 48% at 1010 nm, a detectivity of 1.25 × 1013 Jones and a responsibility of 0.40 A W−1 at 1010 nm. To the best of the authors' knowledge, this is one of the best performed devices reported to date for binary NIR OPDs with response beyond 1000 nm. This study provides a feasible molecular design strategy to develop narrow‐bandgap NFAs with spiro‐conjugation for highly detective NIR OPDs.

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“…Eventually, two novel NFAs, DPA-4F and TPA-4F, (Figure f) based on DPADT and TPADT core units are designed and synthesized according to the procedures shown in Scheme S1. The key compounds DPADT and TPADT could be facilely synthesized by two simple steps according to previous reports. , Then, DPA-4F and TPA-4F were straightforwardly synthesized by sequential Stille coupling and Knoevenagel condensation reactions. The molecular structures of DPA-4F and TPA-4F were fully characterized by nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry.…”

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confidence: 99%

Molecular Order Control of Nonfullerene Acceptors Enables Ultralow Dark Current and High Responsivity in Short-Wavelength Infrared Organic Photodetectors

Shao,

Yang,

Huang

et al. 2024

Chem. Mater.

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Developing organic semiconductors for short-wavelength infrared (SWIR) organic photodetectors (OPDs) remains challenging due to the trade-off between achieving a long-wavelength spectral response and high external quantum efficiencies (EQEs) as well as low dark current densities (J d). Herein, two spiro-structural nonfullerene acceptors (NFAs) with responses reaching 1200 nm, namely DPA-4F and TPA-4F, were developed. By changing the substituent on the spiro-core unit from a hexyl chain to a phenyl group, TPA-4F displayed an ordered three-dimensional stacking network with “head-to-tail” interactions between terminal groups and “core-to-core” interactions between spiro-core units. The enhancement in the molecular order of TPA-4F was demonstrated to effectively red-shift the spectral response, decrease the energetic disorder, and reduce the trap density of states in OPDs. Consequently, a high EQE of more than 40% from 600 to 1060 nm at 0 V bias and a low J d of 2.61 × 10–10 A/cm2 at −0.1 V could be simultaneously realized for TPA-4F-based devices, resulting in a detectivity (D*) exceeding 1013 Jones, ranked the highest value for SWIR OPDs. Furthermore, the obtained OPDs can be integrated into flexible large-area photoplethysmography sensors for pulse signal monitoring even without external SWIR light irradiation. These findings shed light on the design of NFAs for highly detective SWIR OPDs in practical applications.

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Intrinsic photogeneration of long-lived charges in a donor-orthogonal acceptor conjugated polymer

Abstract: Efficient charge photogeneration in conjugated polymers typically requires the presence of a second component to act as electron acceptor. Here, we report a novel low band-gap conjugated polymer with a...

Cited by 6 publications

References 65 publications

Generating Long-Lived Triplet Excited States in Narrow Bandgap Conjugated Polymers

Generating Long-Lived Triplet Excited States in Narrow Bandgap Conjugated Polymers

Spiro‐Conjugation in Narrow‐Bandgap Nonfullerene Acceptors Enables Broader Spectral Response and Higher Detectivity for Near‐Infrared Organic Photodetectors

Molecular Order Control of Nonfullerene Acceptors Enables Ultralow Dark Current and High Responsivity in Short-Wavelength Infrared Organic Photodetectors

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